Working tool, in particular rammer for soil compaction

ABSTRACT

A working tool, in particular a soil rammer or a hammer, has two masses that may be linearly moved back and forth with respect to one another, namely a top mass which comprises a driving motor and a ramming or striking working mass which can be moved by the motor relative to the top mass by means of a crank drive and a set of springs. In order to reduce as much as possible the displacement of the top mass, an additional counterweight can be moved by the motor over at least a large part of the path of displacement of the working mass in the opposite direction thereto. The displacement of the end of the set of springs linked to the crank drive and the displacement of the counterweight are preferably offset relative to one another, with respect to the crank angle, by 180° minus a phase shift derived from the construction parameters of the set of springs.

CROSS-REFERENCE TO A RELATED APPLICATION

[0001] This application is a divisional of commonly assigned U.S. patentapplication Ser. No. 09/402,846, filed in the name of the inventor namedin this application on Oct. 8, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a working appliance, in particular atamper for soil compaction or a hammer, with a tamping or beatingworking mass driven linearly back and forth, via a crank mechanism and aspring assembly, by a motor belonging to the upper mass.

[0004] 2. Discussion of the Related Art

[0005] Known tampers of this type are designed in such a way that theupper mass comprises approximately two thirds and the beating workingmass or lower mass one third of the entire tamper mass, whilst thedistances covered in each case by the upper mass and the working massare in inverse ratio to one another. In this case, the movement of theupper mass is of the order of magnitude of 25 to 30 mm.

[0006] This movement of the upper mass at a frequency of 10-11 Hz hasadverse effects, because these vibrations are transmitted to the body ofthe person controlling the working appliance via a control handle, inparticular to the person's hand and arm.

[0007] Although this transmission of vibrations to the body can for themost part be damped by the skillful attachment of rubber elements, thereare nevertheless also high loads on the mounted drive motor, regardlessof its design.

[0008] This problem also arises when the working appliance is mounted onother appliances or vehicles which may be seriously damaged by thevibrations occurring.

[0009] The output of the tamping system depends largely on the uppermass, since too great a working mass or too high a speed of the workingmass moves the upper mass excessively and aggravates the problemsdescribed above.

[0010] These harmful effects can be partly inhibited by increasing theupper mass, but in this case the overall weight of the tamper isincreased and the power consumption of the drive motor consequentlyrises.

[0011] DE-A 1 925 870 discloses a tamping appliance, in which a tampingfoot can be driven, via a double crank mechanism, by a motor belongingto an upper mass. The drive power is distributed via gearwheels to twointermeshing crank disks which, via associated connecting rods, in eachcase drive rods connected to the tamping foot. Centrifugal weights arefastened in each case to the oppositely rotating crank disks, in such away that the horizontal components of the centrifugal forces cancel oneanother, whilst the vertical components are added together andcounteract the vibration acting on the tamper housing due to thevibration of the tamping foot. The arrangement described has to have abulky design due to the provision of two rods connecting the upper massto the tamping foot and due to the meshing crank disks. The overallweight of the tamper is considerable.

OBJECTS AND SUMMARY OF THE INVENTION

[0012] The object on which the invention is based is, without anyappreciable increase in the overall mass, to achieve substantialstabilization of the upper mass, whilst ensuring that the workingappliance has a compact design.

[0013] In accordance with the invention, this object is achieved byproviding a working appliance having a countermass that counteractsvibrations induced by operation of the working mass. The countermass,which can be driven in rotation by the motor that drives the workingmass, includes first and second centrifugal weights that rotate inopposite directions to one another. The first centrifugal weight whichmay be provided on the crank mechanism itself, rotates about an axis ofrotation that is coaxial with the crank mechanism. The secondcentrifugal weight rotates about an axis of rotation that is at leastessentially coaxial to the axis of rotation of the crank mechanism.However, the axis of rotation of the second centrifugal weight may beoffset in the direction of working mass reciprocation from the axis ofrotation of the crank mechanism and the first centrifugal weight.

[0014] The working appliance is defined in that the second centrifugalweight is arranged rotatably about an axis of rotation arrangedessentially coaxially to the axis of rotation of the crank mechanism.The first centrifugal weight is coaxial with or seated directly on theaxis of rotation of the crank mechanism, and the second centrifugalweight is arranged behind the first centrifugal weight and hasapproximately the same flywheel moment as the first centrifugal weight.The second centrifugal weight is driven in the opposite direction to thefirst centrifugal weight about an axis of rotation that is offsetsomewhat relative to the axis of rotation of the crank mechanism andparallel to the direction of movement of the working mass.

[0015] In another embodiment of the invention the countermass can bemoved linearly back and forth, parallel to the direction of movement ofthe working mass, with a phase shift unequal to 180° in relation to themovement of the working mass.

[0016] The upper mass is pressed upward by a crank mechanism at themoment when the crank mechanism presses the working mass and, therefore,the tamping foot downward via the connecting rod of said crankmechanism, a guide piston and a spring assembly. The result of thespring assembly is that, during the downward movement of the guidepiston, the springs are first tensioned, so as to absorb energy,whereupon, with a delay caused thereby, they subsequently discharge thestored energy again for the downward load on the tamping foot. Thisdelay must be taken into account when the movement of the countermass isto be coordinated as accurately as possible with the movement of theworking mass. When the working mass is drawn upward again by the crankpin of the crank mechanism, the upper mass is moved downward.

[0017] In a further advantageous refinement, therefore, the movement ofthe spring assembly end connected to the crank mechanism and themovement of the countermass are offset relative to one another withrespect to the crank angle by 180° minus a phase shift derived from thedesign parameters of the spring assembly.

[0018] By means of the crank mechanism, an oscillating movement of theupper mass relative to the working mass is built up, and only when thecrank connected to the spring assembly goes past its vertex facing thespring assembly is the energy stored until then in the spring assemblyreleased as tamping or beating energy, so that the countermovement ofthe countermass for damping the movement of the upper mass is requiredonly at this moment, that is to say the movement of the countermass intoits position furthest away from the working mass is to take place onlywhen the crank connected to the spring assembly has passed through thisvertex facing the spring assembly. This is achieved by means of thephase shift described above, which, in practice, must be coordinated atleast approximately with the design parameters.

[0019] According to an expedient refinement, the countermass is guidedon the upper mass in parallel with the direction of movement of theworking mass. In this case, in an advantageous embodiment, thecountermass is driven by a compensating eccentric on the crankmechanism, specifically, for example, via a connecting rod. According toanother expedient refinement, the connection between the countermass andthe compensating eccentric may be designed as a slider crank.

[0020] According to another expedient variant, the countermass consistsof two part masses arranged in each case on one side of the crankmechanism and the other at approximately the same height with respect tothe axis of rotation of the crank mechanism, and each part mass isdriven by an eccentric pin on an eccentric disk assigned to the partmass and rotatably coupled to the crank mechanism, the connectionbetween the eccentric pin and the associated part mass being designed ineach case as a slider crank.

[0021] In a further advantageous variant, the countermass consists offlyweights which are mounted on the upper mass rotatably about mutuallyparallel axes and are driven in rotation in opposite directions by thecrank mechanism and the flywheel moment and mutual phase relationship ofwhich are organized in such a way that they generate an oscillationdirected in counteraction to the working mass, a further refinementbeing that the countermass consists of two centrifugal weights which arearranged symmetrically to the direction of movement of the working massnext to one another at about the same height in this direction and whichare directly coupled to one another so as to be rotatable in oppositedirections and are driven by the crank mechanism.

[0022] In another expedient embodiment for avoiding lateral forces, thecountermass consists of a first centrifugal weight seated directly onthe shaft of the crank mechanism and of two second centrifugal weightsarranged symmetrically to the direction of movement of the working massnext to one another at about the same height in this direction andhaving flywheel moments equal to one another, such centrifugal weightsbeing driven rotatably by the crank mechanism in the opposite directionto the first centrifugal weight and their flywheel moment in each casebeing about half the flywheel moment of the first centrifugal weight.

[0023] In yet another variant, the countermass consists of a firstcentrifugal weight seated directly on the axis of rotation of the crankmechanism and of a second centrifugal weight which is arranged behindsaid first centrifugal weight and which has about the same flywheelmoment as the first centrifugal weight and which is driven in theopposite direction to the first centrifugal weight about an axis ofrotation offset somewhat, parallel to the direction of movement of theworking mass, relative to the axis of rotation of the crank mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention is explained in more detail by means of thefollowing description of its exemplary embodiments illustrated in thedrawing in which:

[0025]FIG. 1 shows a side view of a first embodiment of a tamperdesigned according to the invention, transversely to the crank axis,partly in a section taken in a plane containing the crank axis;

[0026]FIG. 2 shows a section of a detail through the housing of thecrank mechanism of the embodiment shown in FIG. 1, in a plane at rightangles to the crank axis;

[0027]FIG. 3 shows a view, similar to that of FIG. 1, of the upper endof a tamper according to a second embodiment;

[0028]FIG. 4 shows a sectional view, similar to that of FIG. 2, of thesecond embodiment;

[0029]FIG. 5 shows a sectional view, similar to that of FIG. 4, in thecase of a third embodiment;

[0030]FIG. 6 shows a sectional view, similar to that of FIG. 4, in thecase of a fourth embodiment;

[0031]FIG. 7 shows a sectional view, similar to that of FIG. 4, in thecase of a fifth embodiment;

[0032]FIG. 8 shows a view, similar to that of FIG. 3, of the upper endof a tamper according to a sixth embodiment; and

[0033]FIG. 9 shows a view, similar to that of FIG. 4, of the sixthembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In the tamper shown in FIG. 1, and designated as a whole by 10,the control handle is not illustrated for the sake of clarity. Thetamper 10 terminates at the bottom in a tamping foot 12 which canexecute a back-and-forth movement in the direction of the movement axis16 relative to the crank housing 14 shown in the upper region of thetamper 10, the outer cladding of the appliance therefore having aconcertina-like portion 18 consisting of elastic material.

[0035] A drive motor 20 is fastened to one side of the crank housing 14,said drive motor driving a drive shaft 22 provided with a toothed pinion24 which is in engagement with a circumferentially toothed crank disk26. The crank disk 26 carries two crank pins 28 and 30 (FIG. 2) offsetat approximately 180°. The crank pin 28 is connected, via a yoke-shapedconnecting rod 32 surrounding the drive shaft 22, to a guide piston 34which is arranged movably in the direction of the axis 16 in a pistonguide 36 connected to the crank housing 14 and, being concealed in FIG.1 by the concertina-like portion 18, is connected to the tamping foot 12via a spring assembly. Connected via a connecting rod 38 to the crankpin 30 serving as a compensating eccentric is a piston 40 which islikewise arranged movably in the direction of the axis 16 in a pistonguide 42 and, together with the connecting rod 38, forms thecountermass, provided according to the invention, to the working mass.

[0036] An angular distance of 180° is shown in FIG. 2 between the crankpins 28 and 30. The piston or countermass 40 would consequently reachtop dead center when the guide piston 34 connected to the springassembly, not shown, reaches its bottom dead center. For the reasonsalready described, however, the piston 40 is to reach top dead centerwith a time delay, depending on the design features of the springassembly, and therefore the angular distance must be selected smallerthan 180° by the amount of a particular phase shift angle. In practice,this phase shift angle may be 70-100°.

[0037] In the variant illustrated in FIGS. 3 and 4, the crank disk 26 ₁,in engagement with the toothed pinion 24 ₁, on the drive shaft 22 ₁ isprovided with a crank 29 bent so as to form the crank pins 28 ₁ and 30₁. The crank pin 28 ₁, which forms the free end of the crank 29, engagesinto a sliding block 31 arranged dispaceably in a guide slot 33 formedin a piston 40 ₁ serving as a countermass. The piston 40 ₁ is guidedmovably parallel to the axis of movement 16 in a guide 42 ₁ formed onthe crank housing 14 ₁. The connecting rod 32 ₁, configured forconnection to the guide piston (not shown) and transmitting the movementto the spring assembly, is mounted on the crank pin 28 ₁. Thefunctioning of this variant corresponds largely to the design accordingto FIGS. 1 and 2. However, because the countermass is driven by a slidercrank mechanism, this embodiment makes it possible to have a designwhich is shortened in the direction of the axis of movement 16.

[0038]FIG. 5 shows a variant which likewise provides a slider crankdrive for the countermass, the arrangement making further shorteningpossible. The crank disk 26 ₂, provided with the crank pin 28 ₂ for theconnecting rod 32 ₂ for the transmission of movement to the springassembly, is connected fixedly in terms of rotation to a gearwheel 35which is arranged coaxially to the crank disk and with which twocircumferentially toothed eccentric disks 37 and 39 are in engagement onboth sides of the axis of movement 16 and are the same height withrespect to the latter. The eccentric disks each carry an eccentric pin30 a ₂ and 30 b ₂ which engage into guide slots 33 a ₂ and 33 b ₂,assigned to them, of two identically designed pistons 40 a ₂ and 40 b ₂which together form the countermass, which are mounted displacablyparallel to the axis of movement in guides 42 a ₂ and 42 b ₂ assigned tothe pistons and formed on the crank housing 14 ₂.

[0039] The following variants replace the linearly movable countermassby rotating flyweights.

[0040] In the variant according to FIG. 6, a gearwheel 35 ₃ is connectedfixedly in terms of rotation and coaxially to the crank disk 26 ₃ forthe purpose of actuating the connecting rod 32 ₃. Two toothed disks 37 ₃and 39 ₃ of the same size and the same number of teeth, which are inengagement with one another, are arranged on both sides of the axis ofmovement 16, at the same distance from the latter and at the same heightwith respect to this, said toothed disks in each case being providedwith a centrifugal weight 41 and 43. The toothed disk 37 ₃ is connectedfixedly in terms of rotation and coaxially to a gearwheel 45 which is inengagement with the gearwheel 35 ₃ having the same number of teeth, sothat the two centrifugal weights 41 and 43 move in opposition to themovement of the connecting rod 32 ₃ in a predetermined phaserelationship. At the same time, the centrifugal weights 41 and 43 arearranged in such a way that their positions are in each case locatedopposite to one another mirror-symmetrically relative to the axis ofmovement 16. This avoids both lateral forces, such as are caused by theoblique connecting rod 38 in the embodiments according to FIGS. 1 and 2,and frictional losses in the guides 33, 33 a ₂ and 33 b ₂ according toFIGS. 3 to 5.

[0041] The variant according to FIG. 7 shows a flyweight acting in onlyone direction and located on the crank mechanism and two flyweightswhich are opposed to said flyweight and which provide mass compensationand therefore also prevent any lateral movement. The flyweight on thecrank mechanism is represented by the centrifugal weight 47 on the crankdisk 26 ₄. Two disks 37 ₄ and 39 ₄ identical in diameter to the crankdisk 26 ₄ and provided with centrifugal weights 41 ₄ and 43 ₄ arearranged symmetrically to the axis of movement. The three disks 26 ₄, 37₄ and 39 ₄ are connected to one another for joint movement by means of anon-slip gear connection, for example a chain 51, in such a way that thetwo disks 37 ₄ and 39 ₄ move in the same direction of rotation, but inopposition to the crank disk 26 ₄.

[0042]FIGS. 8 and 9 show a final variant which is a development of thevariant according to FIG. 7 in as much as the two disks 37 ₄ and 39 ₄rotating in the same direction are replaced, in this case, by a singledisk 53. The disk 53, which is offset relative to the crank disk 26 ₅ inthe direction of working mass reciprocation, is driven in opposition tothe crank disk 26 ₅ from the drive shaft 22 ₅ via a specific pinion 55and an intermediate wheel 57. A centrifugal weight 59 is provided on thedisk 53 and, therefore, is arranged rotatably about an axis of rotationthat is offset from the axis of rotation of the crank disk 26 ₅. Anothercentrifugal weight 61 is mounted directly on the crank disk 26 ₅ and,therefore, rotates about the axis of the crank disk 26 ₅. Alternatively,disk 53 could be configured to rotate about an axis that is at leastessentially coaxial with the axis of crank disk 26 ₅.

I claim:
 1. A working appliance, comprising: a working mass which can bedriven linearly back and forth, via a crank mechanism, by a motorbelonging to an upper mass; and a countermass which, driven by themotor, can be moved; wherein the countermass can be moved linearly backand forth, parallel to the direction of movement of the working mass,with a phase shift unequal to 180° in relation to the movement of theworking mass.
 2. The working appliance as claimed in claim 1, whereinthe countermass is driven by a compensating eccentric on the crankmechanism.
 3. The working appliance as claimed in claim 1, wherein thecountermass consists of two part masses which are driven in each case byan eccentric pin on a respectively associated eccentric disk coupledrotatably to the crank mechanism.
 4. A working appliance comprising: amotor; a crank mechanism; a working mass which can be driven toreciprocate linearly back and forth by the motor via the crankmechanism, wherein the motor comprises part of an upper mass of theworking appliance; and a countermass which can be driven by the motor tomove linearly back and forth, parallel to the direction of movement ofthe working mass, with a phase shift unequal to 180° in relation to themovement of the working mass.
 5. The working appliance as claimed inclaim 4, further comprising a compensating eccentric that is located onthe crank mechanism an that drives the working mass.
 6. The workingappliance as claimed in claim 4, wherein the countermass comprises twopart masses, each of which is driven by an eccentric pin on arespectively associated eccentric disk coupled rotatably to the crankmechanism.